The primary objective of the proposed research is to investigate the mechanism of action of ASTA Z 7557 (mafosfamide) by determining absolute AUC values for 4-hydroxycyclophosphamide and phosphoramide and phosphoramide mustard in plasma of mice treated with this new, pre-activated cyclophosphamide congener (mafosfamide), as a means of discerning which of these two tumor-active metabolites is chiefly responsible for mediating the anticancer activity of the new agent. The specific aims include synthesis of H3-ASTA Z 7557; pharmacokinetic studies of parent drug, 4-hydroxycyclophosphamide mustard; determination of urinary excretion of ASTA Z 7557 and its tumor-active metabolites; and tissue distribution studies as a means of identifying organ-specific accumulation of active metabolites. The primary methodology involves solvent extraction and thin-layer chromatographic isolation of radioactive drug and metabolites for facile quantitation. The proposed research is designed to serve as a model study for ultimate investigations in patients for the purpose of determining whether ASTA Z 7557 (a) generates high plasma levels of 4-hydroxycyclophosphamide or of phosphoramide mustard as an indication of the likely, dominant tumor-active blood-transported, metabolite and, consequently, (b) may be expected to be similar to or different from cyclophosphamide in its spectrum of antitumor activity in man.